1. Field of the Invention
The present invention relates generally to pharmaceutical compositions and more specifically to improved formulations for use with therapeutic polypeptides.
2. Description of Related Art
Advances in genetic engineering technologies have made a wide variety of biologically active polypeptides available in sufficiently large quantities for use as drugs. Such polypeptides, however, can lose biological activity by a variety of chemical and physical means including deamidation, aggregation and denaturation. Consequently, the identification of buffer systems that stabilize these agents is essential for the optimization of their therapeutic benefits.
Stable formulations of therapeutic agents are particularly important for use in delivery devices that expose these agents to elevated temperatures and/or mechanical stress. Stable insulin formulations, for example, are required for use in continuous infusion systems and related devices. In continuous infusion systems, a fluid containing a therapeutic agent is pumped from a reservoir, usually to a subcutaneous, intravenous, or intraperitoneal depot. Formulations of polypeptides such as monomeric insulin analogs for use in continuous infusion systems must remain soluble and substantially free of aggregation, even though subjected to the patient""s body heat and motion for periods ranging from a few days to several months. In this context, instability is promoted by the higher protein concentrations that are desirable for continuous infusion systems and by the thermo-mechanical stress to which formulations are exposed in continuous infusion systems. Therefore, improvement in the physical and chemical stability of concentrated insulin analog formulations is urgently needed to facilitate their use in continuous infusion systems. In particular, insulin formulations for implantable pump use must possess chemical and physical stability in the harsh environment of the implantable pump. The formulations must be stable during long term (90 days) storage at elevated temperature (37-40xc2x0 C.) with constant agitation on a relatively hydrophobic surface (e.g. TiO2 with an average contact angle of more than 60xc2x0).
As noted above, monomeric insulin analog formulations have a propensity to aggregate and to become unstable when exposed to thermo-mechanical stress. Aggregation may even be manifested as precipitation of higher-order insulin species. In this way, aggregation can prevent reproducible delivery of effective therapeutic doses of monomeric insulin analogs, and may also cause irritation at the administration site or more systemic immunological response. Consequently, insulin analog formulations stabilized against aggregation are desirable.
While a number of aqueous formulations which stabilize polypeptide compositions have been identified in the art, the destabilization of polypeptides in solution continues to create problems for medical practitioners. Consequently, there is a need for new pharmaceutical compositions which overcome the problems of the prior art. This need is fulfilled by the invention that is described below.
The present invention is a pharmaceutical composition that enhances the stability of polypeptides in an aqueous medium. Typically the composition includes a polypeptide that is prone to aggregation stabilized by a mixed buffer system. The invention relates to the discovery that a mixed TRIS buffer system provides improvements in the stabilization of polypeptides by inhibiting the aggregation of polypeptide pharmaceuticals. Specifically, by using TRIS to supply the negative coefficient of pH in combination with buffering molecules that: (1) can react with CO2 and (2) have no free amine group, a formulation that provides enhanced polypeptide stability is obtained. In typical illustrative embodiments of the invention for example, one can use TRIS with acetate, phosphate or citrate buffers at the appropriate pH.
The invention described herein has a variety of embodiments. An illustrative embodiment consists of a solution formulation comprising including a physiologically tolerated mixed buffer system comprising TRIS combined with a buffering molecule which both reacts with carbon dioxide; and does not contain a free amine group, a polypeptide, zinc; and a phenolic preservative. In a preferred embodiment of the invention the buffering molecule is selected from the group consisting of acetate, phosphate and citrate. In a highly preferred embodiment, the buffering molecule is phosphate. In a related embodiment of this invention, the formulation further comprises an isotonicity agent and the polypeptide is a monomeric insulin analog selected from the group consisting of LysB28ProB29-human insulin and AspB28 human insulin.
In a specific embodiment of the mixed buffer system described herein, TRIS is present at a concentration of about 1.5 mg/ml to about 4.5 mg/ml; phosphate is present at a concentration of about 0.2 mg/ml to about 2.5 mg/ml, insulin is present at a concentration of about 250 to about 1000 U/ml, zinc is present at a concentration of about 0.07 xcexcg/ml to about 0.09 xcexcg/ml, m-cresol is present at a concentration of about 2.2 mg/ml, phenol is present at a concentration of about 0.9 mg/ml and glycerol is the isotonicity agent and is present at a concentration of about 16 mg/ml. In a preferred embodiment, TRIS is present at a concentration of about 2 mg/ml to about 3 mg/mil and phosphate is present at a concentration of about 0.5 mg/ml to about 1.5 mg/ml.
Yet another embodiment of the invention consists of a stable, soluble formulation of a monomeric insulin analog for use in a continuous infusion system, comprising: an isotonicity agent; a mixed buffer system consisting essentially of TRIS combined with a buffer selected from the group consisting of phosphate buffer, acetate buffer and citrate buffer; a monomeric insulin analog; zinc; and a phenolic preservative.
Yet another embodiment of the invention consists of a method for treating diabetes comprising administering an effective dose of the above-mentioned formulation to a patient in need thereof. A related embodiment of the invention consists of a method for treating hyperglycemia comprising administering an effective dose of the formulation to a patient in need thereof. In a preferred embodiments of these methods, the formulation is administered using a continuous infusion system
Another embodiment of the invention disclosed herein includes a process for preparing the formulation by combining a physiologicaliy-tolerated mixed buffer system comprising TRIS combined with a buffer selected from the group consisting of phosphate buffer, acetate buffer and citrate buffer; with a polypeptide prone to aggregation; zinc; and a phenolic preservative. Yet another embodiment of the invention is a method of stabilizing a polypeptide prone to aggregation comprising combining the peptide with a physiologically-tolerated mixed buffer system comprising TRIS mixed with a buffering molecule that does not contain a free amine group and which absorbs carbon dioxide and counteracts the effects of this molecule on pH; zinc; and a phenolic preservative.